I can highly recommend the following places.....
The Boathouse - Very nice Drinks/lunch in Central Park
Grand Central Station - Architecturally stunning
Guggenheim - Nuff said
Ellis Island... Very interesting, worth a stop if you go to Liberty Island
Greenwich Village - If you fancy a potter about
5th Avenue - Shopping
Ground Zero - Every one should go there out of respect
Madison Square Garden - Go watch a Basketball Match - Its much better than it sounds
There is tons to do and see, I have been 3 times and still have places I want to go.